Presently available absorbent articles such as diapers, sanitary napkins, incontinence briefs, and the like are generally very good at absorbing aqueous fluids such as urine and blood. However, during typical use such articles become saturated at the impingement zone while other zones removed from the impingement zone will remain dry. As a result, a substantial portion of the total absorbent capabilities of such articles remains unused. Thus, it would be highly desirable to have a means for transporting the aqueous fluids from the impingement zone to other areas of the absorbent article to more fully utilize the article's total absorbent capability. We have discovered such a means by the use of certain fibers that are capable of transporting aqueous fluids on their surfaces.
Liquid transport behavior phenomena in single fibers has been studied to a limited extent in the prior art (see, for example, A. M. Schwartz & F. W. Minor, J. Coll. Sci., 14, 572 (1959)).
There are several factors which influence the flow of liquids in fibrous structures The geometry of the pore-structure in the fabrics (capillarity) the nature of the solid surface (surface free energy, contact angle), the geometry of the solid surface (surface roughness, grooves, etc.), the chemical/physical treatment of the solid surface (caustic hydrolysis, plasma treatment, grafting, application of hydrophobic/hydrophilic finishes), and the chemical nature of the fluid all can influence liquid transport phenomena in fibrous structures.
The ability to transport liquids (alternately referred to herein as "wickability") and to hold liquids are two important features of absorbent cores of sanitary consumer disposables such as diapers, adult incontinent products, and feminine hygiene products. Absorbent cores are designed to wick fluids as far as possible to prevent leakage and optimize the use of absorbent material. In a conventional diaper, fluid is wicked by capillary action through the porous fluff pulp core. Liquid holding capacity is largely within the pores of the fluff pulp but is also enhanced by the addition of superabsorbent polymers to the absorbent core. These superabsorbent polymers are especially beneficial for holding liquids under pressure compared to pulp alone. Absorbent cores of diapers and adult incontinent products do not sufficiently wick fluids from the crotch area to entirely prevent leaking Typically 3-7% of diapers, approximately 30% of feminine napkins, and 33-40% of adult incontinent products leak. Leaking is the number one customer complaint about these products. Solving the leaking problem is high priority among the manufacturers of these products.
In the prior art, thermally bonded webs composed of polyester, polypropylene, or polyethylene hydrophobic fibers are formed. These webs are subsequently coated with acrylic acid partially neutralized by alkali metallic salts and crosslinked simultaneously with polymerization to form webs coated in situ with superabsorbent polymer (European Patent Application 0 223 908). The webs have increased absorption of fluid when used in a sanitary product such as a diaper, but the individual fibers of the web do not possess the ability to wick fluid from the crotch area (which is most prone to leaking) to lesser utilized areas of the absorbent core.
French Patent 955,625, Paul Chevalier, "Improvements in Spinning Artificial Fiber", published Jan. 16, 1950, discloses fibers of synthetic origin with alleged improved capillarity. The fibers are said to have continuous or discontinuous grooves positioned in the longitudinal direction.
Japanese Patent Laid-Open No. 204,975/1984 describes the coating of cellulose fiber based material with a water soluble monomer which is converted into a water-absorptive polymer. According to U.S. Pat. No. 4,721,647, this type of material has poor absorption performance because the monomer is able to penetrate inside the fiber base material and fill the capillaries between filaments. The mode of wicking in this prior art is totally in the capillaries between the fibers. The diameter of the capillaries is reduced by the coating. As the coating swells in the wet state, the capillaries are blocked off.
Also, the art discloses various H-shapes as follows:
U.S. Pat. No. 3,121,040 entitled "Unoriented Polyolefin Filaments" dated Feb. 11, 1964; PA1 U.S. Pat. No. 3,650,659 entitled "Spinning Die" dated Mar. 21, 1972; PA1 U.S. Pat. No. 870,280 entitled "High Bulk Filamentary Material" dated Jun. 14, 1961; PA1 U.S. Pat. No. 4,179,259 entitled "Spinneret for the Production of Wool-like Man-Made Filament" dated Dec. 18, 1979; PA1 U.S. Pat. No. 3,249,669 entitled "Process for Making Composite Polyester Filaments" dated Mar. 16, 1964; PA1 U.S. Pat. No. 3,623,939 entitled "Crimped Synthetic Filament Having Special Cross-Sectional Profile" dated Jun. 28, 1968; PA1 U.S. Pat. No. 3,156,607 entitled "Lobed Filament" dated Nov. 10 1964; PA1 U.S. Pat. No. 3,109,195 entitled "Spinneret Plate" dated Nov. 5, 1963; PA1 U.S. Pat. No. 3,383,276 entitled "Extruded Synthetic Filament" dated Mar. 10, 1964; PA1 Netherlands Abstract OCTROO1N.sup.o 8490, Aunvrage No. 18049, dated Nov. 28, 1922. PA1 .theta..sub.a is the advancing contact angle of water measured on a flat film made from the same material as the fiber and having the same surface treatment, if any, PA1 X is a shape factor of the fiber cross-section that satisfies the following equation ##EQU1## wherein P.sub.w is the wetted perimeter of the fiber, r is the radius of the circumscribed circle circumscribing the fiber cross-section, and D is the minor axis dimension across the fiber cross-section PA1 .theta..sub.a is the advancing contact angle of water measured on a flat film made from the same material as the fiber and having the same surface treatment, if any, PA1 X is a shape factor of the fiber cross-section that satisfies the following equation ##EQU2## wherein P.sub.w is the wetted perimeter of the fiber, r is the radius of the circumscribed circle circumscribing the fiber cross-section, and D is the minor axis dimension across the fiber cross-section. PA1 .theta..sub.a is the advancing contact angle of water measured on a flat film made from the same material as the fiber and having the same surface treatment, if any, PA1 X is a shape factor of the fiber cross-section that satisfies the following equation ##EQU3## wherein P.sub.w is the wetted perimeter of the fiber, r is the radius of the circumscribed circle circumscribing the fiber cross-section, and D is the minor axis dimension across the fiber cross-section, PA1 and wherein the uphill flux value of said fiber is from about 2 to about 60 cc/g/hr when measured from a reservoir of synthetic urine test fluid along a 20 cm long ramp to an absorbent on an attached platform at 10 cm height. PA1 .theta..sub.a is the advancing contact angle of water measured on a flat film made from the same material as the fiber and having the same surface treatment, if any, PA1 X is a shape factor of the fiber cross-section that satisfies the following equation ##EQU4## wherein P.sub.w is the wetted perimeter of the fiber, r is the radius of the circumscribed circle circumscribing the fiber cross-section, and D is the minor axis dimension across the fiber cross-section, with the proviso that the fiber is not an X-shaped or an H-shaped fiber having a .theta..sub.a of about 22 degrees, cos .theta..sub.a of about 0.9, and an X factor of about 1.8.
U.S. Pat. No. 4,707,409 entitled "Spinneret Orifices and Four-Wing Filament Cross-Sections Therefrom" dated Nov. 17, 1987, assigned to Eastman Kodak Company, describes a spinneret having an orifice defined by two intersecting slots. Each intersection slot is in turn defined by three quadrilateral sections connected in series.
Further, PCT International Publication No. WO90/12/30, published on Oct. 18, 1990, entitled "Fibers Capable of Spontaneously Transporting Fluids" by Phillips et al. discloses fibers that are capable of spontaneously transporting water on their surfaces and useful structures made from such fibers.
Also, conventional crimping of fibers is done mechanically with a stuffer box crimper. This method can damage or distort the cross-section of the fibers of this invention. This distortion of the cross-section reduces the ability of the fiber to move and hold fluids.
There are various methods of helically crimping a fiber in the art. For example, U.S. patent application Ser. No. 07/333,651 abandoned describes crimped staple fibers and the process for making the fibers. U.S. Pat. No. 3,050,821 describes a high bulk textile material after a relaxing treatment. U.S. Pat. No. 3,681,188 describes a poly(trimethylene terephthalate) textile fiber in a helical crimp form. U.S. Pat. No. 3,584,103 describes a process for making a helically crimped poly(trimethylene terephthalate) fiber with asymmetric birefringical across the diameter of the filament. U.S. Pat. No. 3,623,939 discloses a crimped synthetic filament. The H-shaped cross-section of the fiber is shown.
We have discovered fibers that have a unique combination of properties that allows for spontaneous transport of aqueous fluids such as water on their surfaces. Heretofore, fibers capable of spontaneously transporting aqueous fluids such as water have been unknown. These fibers can be coated with superabsorbing polymers which are capable of absorbing liquid as well as transporting liquid. Even more preferably, fibers having both a major and minor symmetrical axis are quenched by air where the air stream is perpendicular to the major axis of the fiber.